Finally dealt with Lunatic Ursula. Ended up doing a slightly different version of what that "free units only" strategy used (although pretty sure I would've figured it out regardless since I have a high level Subaki and that's the obv chokepoint)-- big difference is I had Kagero so I could instantly kill one of the two ninja to start (move her to the bottom square in your start area and she'll counterhit the ninja dead while being left at 1 hp).
Meanwhile heal her up and have Robin F whittle away at the axe knight after counterhitting Ursula dead. Then move full health kagero into the slot where Subaki is tanking to kill the ninja sniping at him at the same turn Robin F finishes off the axe knight. She can tank one shot from the Cavalier who is the only one remaining at this point
Basically a lot more efficient version of the free strategy but you know you can afford to do that with better units.
Team was Kagero 5* L40, Serra 5* L27, Robin 4* L36, Subaki 4* L38. Subaki had an Iron Lance instead of the Sapphire Lance so I had more turns to get everyone in position.
No problem!
This is a cute and pop genocide of love!